Epoxy resin as binder and coating has a large global market, but as an industry standard plastic matrix of the manufacture of fiber-reinforced plastics (FRP). FRPs are composite materials composed by a polymer matrix and fibers such as carbon fibers, glass fibers, aramid fibers, natural fibers or other fibers. Fiber helps to enhance the strength, elasticity and other aspects of performance of plastics. FRPs are also commonly referred to as “plastic composite material,” or simply as “composite material.” “Plastic composite material” also includes non-fibrous materials such as metal or nanomaterials. Plastic composite material can be used as lightweight alternatives for other structural materials (such as steel or aluminum), which are widely used in automotive, aerospace, marine craft, wind energy, and sporting goods industries. Lightweight composite material help to improve energy efficiency, which has significant environmental benefits, however, the persistence and limits of recycling of thermoset plastic composite material in the environment offset its positive impact. On the growing wind power can be predicted to cause accumulation of garbage of industrial waste materials will be a typical example.
The most common epoxy resin formula contains a diepoxide resin (resin) and the polyamine compound (curing agent), essentially may form infinite molecular weight, cross-linked polymer network structure. The combination of “resin” and “curing agent” is sometimes referred to as “cured epoxy resin”, “cured resin” or simply called “resin” or “epoxy resin.” The wide range of applications of epoxy resin formula of the composite material is due to its excellent processability before curing properties and excellent adhesion, mechanical strength, thermal dispersion, electrical properties, chemical resistance after curing. In addition, high density and three-dimensional network structure of the epoxy resin after curing make it extremely hard and durable material that can withstand a wide range of environmental conditions' influence. Meanwhile, the cross-linked structure of cured epoxy resin makes it particularly difficult to remove, recycling and reuse. Essentially, the crosslinking reaction of a polyamine compound with an epoxy resin usually is irreversible, and therefore this material cannot be re-melting, not lossless re-formed and easily dissolved. Degradable latent epoxy resin curing agents are research focus of epoxy resin curing agent home and abroad in recent years. Latent curing agent, is the curing agent added to the epoxy resin and its constituent one-component system have a certain storage stability at the room temperature, and in the heat, light, moisture, pressure and other conditions can quickly curing react. Compared to widely used two-component epoxy resin system nowadays, one-component epoxy resin system mixing prepared by the latent curing agent and epoxy resin has advantages of simplified production operation process, no environmental pollution, large-scale industrial production applications. The research of latent epoxy curing agent are mainly by physical or chemical methods, to improve the curing activity of the general use of low and high temperature curing agent, one is sealing off and passivating the reactivity of some curing agent with high reactivity but poor storage stability, Another is improving and inspiring the reactivity of some curing agent with high storage stability but poor reactivity, Ultimately, make the curing agent have certain storage stability after added to the epoxy resin at room temperature, while using will achieve the purpose of rapid curing by light, heat and other external conditions to release the reactivity of the curing agent.
Epoxy prepreg is a compound system composed of epoxy resin, curing system and the reinforcing fiber, the resin system was an uncured state as an intermediate substrate for preparing the composite. Carbon fiber composite material prepared by the epoxy prepreg has high specific strength and specific modulus, devisable performance and diversity of forming technology, which is widely used in construction materials, aerospace and civilian entertainment.
By 2015, global composites production capacity will significantly increase, and exceed 10 million tons. However, how to deal with and recycle the waste of fiber composites have hindered its booming as a worldwide problem, thereby constraining the sustainable development of fiber composites.
The recovery process of fiber composites have been reported roughly in three ways: landfill, incineration and grinding. Landfilling is burying waste composite materials into the ground directly, which is simple, low cost, but occupy the land and pollution remains the same. While incineration can recover some energy, but the incineration process requires a lot of energy, also it is a problem from environmental point of view. A novel carbon fiber composite material recycling technology allows the plastic matrix composite material to remove by a special incinerator and the residual carbon fibers may be recovered for reuse. Although this approach steps to the direction of the sustainable development, it does not represent completely recycling because the plastic matrix is destroyed during the recycling process and cannot be recycled. Through pulverizing recovering method, the obtained fiber material is reused as additional materials, but if added to a certain percentage, it will reduce related mechanical properties of materials. In general, these methods have their limitations in varying degrees, existing disadvantages of fiber shortening, performance degradation, environmental pollution, and high recycling cost and so on, therefore, effective and feasible method for the recycling of waste composite materials is still a issue to be addressed in composites field.